Variable leading edge stator vane assembly

ABSTRACT

A variable leading edge stator vane assembly, particularly suited for use in a bypass gas turbine engine as a last stage fan stator, includes vane spindles on each end of the movable portion which are rotatably disposed in the gas path walls and which are large relative to the thickness of the airfoil so that they extend downstream of the movable portion; the stationary portion of the vane has its leading edge pinned into cavities positioned on the axis of rotation of the vane spindles and its trailing edge secured directly to the flow path walls.

United States Patent 1 1111 3,887,297 Welchek 1 June 3, 1975 [54] VARIABLE LEADING EDGE STATOR VANE 3,442,493 5/1969 Smith, Jr 415/161 ASSEMBLY FOREIGN PATENTS OR APPLICATIONS [75] Inventor; Michael-h" Welchekt Maiden, 893,054 4/1962 United Kingdom 415/161 conn- 774,501 5/1957 United Kingdom.... l. 415/161 Assignee2 Uni'ed Aircraft corporafiun, East 901,010 H1954 Germany 415/163 Hartford, Conn. Primary Examiner-Henry F. Raduazo Filed: June 1 1974 Attorney, Agent, or Firm-Stephen E. Revis 21 Appl. No.: 432,955

[57] ABSTRACT [52] US. Cl 415/161; 415/148 A variable leading edge stator vane assembly, particu- {51] Int. Cl. F0ld 17/12 larly suited for use in a bypass gas turbine engine as a [581 ie 01 Search last stage fan stator, includes vane spindles on each 164 end of the movable portion which are rotatably disposed in the gas path walls and which are large rela- [56] References Cited tive to the thickness of the airfoil so that they extend UNITED STATES PATENTS downstream of the movable portion; the stationary 2805 818 9/1951 Ferri 415/148 Portion 0f vane has its leading edge Pinned 5 |2H957 Nelson w v I I D /143 cavities positioned on the axis of rotation of the vane 2,833,274 6/1958 Fl mher et a1 415 1 1 spindles and its trailing edge secured directly to the 3,059,902 10/1962 Savonuzzi 415/163 flow path walls. 3,066,488 12/1962 Mock 415/161 3,318,574 5/1967 Tyler 415/148 5 Claims, 3 Drawmg Figures PATH-HER JUE. 3 1975 VARIABLE LEADING EDGE STATOR VANE ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to variable stator vanes and more particularly to variable stator vanes having a movable upstream portion and a stationary downstream portion.

2. Description of the Prior Art In bypass type gas turbine engines there are one or more fan stages upstream of a splitter which separates the incoming air into the fan and primary gas streams. It is desirable that the air enter the fan stream in an axial direction for all engine operating conditions; it is also usually desirable that the angle at which the air enters the first compressor stage be substantially constant for all engine operating conditions. In addition to the foregoing, the angle at which the air leaves the last fan rotor blade is different for different engine operating conditions, such as for takeoff, climb and cruise; for each of the different engine operating conditions there is a preferred angle at which the air should strike the leading edges of the last fan stator vane in order to maximize aerodynamic efficiency. In view of the foregoing considerations a movable upstream portion (i.e., a variable leading edge) and a stationary downstream portion (i.e., a fixed trailing edge) may be the logical design choice for the last fan stator vane.

Stator vanes with movable downstream portions are well known in the art. One example is Fletcher et al U.S. Pat. No. 2,838,274. One of the more common ways of attaching the movable downstream portions of vanes is through the use of spindles disposed at the forward edge thereof which fit into openings and bushings in the gas flow path walls such as is shown in Fletcher et al.

Movable upstream portions of stator vanes are also known in the art although less common than movable downstream portions. One such vane having a movable upstream portion is shown in Ferri U.S. Pat. No. 2,805,818; another is described in Tyler U.S. Pat. No. 3,318,574. Note that in both of these patents (and in Fletcher et al) the spindles or pins on which the movable portion rotates have a diameter which is no greater than the thickness of the airfoil. In some instances, when the gas loads on the vanes are very high and the thickness of the airfoil is relatively small these spindles or pins may not be strong enough to carry the loads. Furthermore, from an aerodynamic standpoint, it may not be desirable to interlock the movable and fixed portions of the vanes such as is shown in both Tyler and Ferri; rather, it is usually more desirable to abut the stationary and movable portions in the manner shown in Fletcher et al to reduce complexity and cost.

SUMMARY OF THE INVENTION A variable stator vane assembly according to the present invention includes an upstream movable portion and a downstream stationary portion, the movable portion being rotatably secured to the gas path walls at each end thereof by relatively large diameter spindles which overhang the downstream edge of the movable portion; the rearward portion of the stationary portion is secured directly to the flow path walls and the leading edge thereof is pinned into cavities in the overhung portion of the spindles.

Analysis of a variable leading edge stator vane in the fan of a gas turbine engine reveals that the loads to be carried by the spindles securing the movable portion to the cases are considerably higher than are the loads on spindles of variable trailing edge vanes. In view of this it may often be required that the spindles for the variable leading edge of the vane be considerably larger in diameter than the thickness of the airfoil and the downstream portion of the spindle will necessarily extend a fair distance downstream of the rearward edge of the movable portion. This means that the leading edge of the stationary portion cannot be rigidly secured to the gas path walls since it is positioned between the rotating spindles. This may result in a vibrational problem. One of the objects of the present invention is the elimination of this vibration problem. This is accomplished by pinning the leading edge of the stationary portion into cavities positioned on the axis of rotation of the spindles.

A further object of the present invention is to maintain a close gap with minimum tolerance between the movable portion and the stationary portion of the airfoil. This may be difficult in prior art designs in view of the fact that the movable and stationary portions may be individually attached to the casing resulting in large tolerance buildups between the two; this would inhibit putting the two portions of the airfoil as close together as one would like. The present invention solves this problem since the forward edge of the fixed portion is located with respect to the downstream edge of the movable portion by pins that fit into cavities machined into the vane spindles, the vane spindles being rigidly attached to or integral with the movable portion of the airfoil.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of a preferred embodiment thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view, partly in section of a variable fan stator vane assembly according to the preferred embodiment of the present invention.

FIG. 2 is a sectional view taken along the line 22 of FIG. 1.

FIG. 3 is a perspective view ofa plug used in the vane assembly of FIG. I, removed from the overall assembly to clearly show its shape.

DESCRIPTION OF THE PREFERRED EMBODIMENT Consider, as an exemplary embodiment of the subject invention, the second stage fan stator assembly 10 of a twostage gas turbine engine fan test rig. The stator assembly 10 includes outer annular casing 12 having an outer surface 14 and inner annular casing 16 having an inner surface 18. The outer and inner surfaces 14, I8 are gas path walls and define an annular gas flow path 20 therebetween. The gases flow in the direction of the arrow 22. The stator vane assembly 10 also includes a plurality of circumferential spaced stator vanes 24, only one of which is shown in the drawing. Each stator vane 24 includes an upstream movable portion 26 and a downstream stationary portion 28. The movable portion 26 includes an airfoil 30, an outer spindle 32 and an inner spindle 34, the spindles 32, 34 being integral with the airfoil 30 in this particular embodiment. The airfoil 30 extends radially across the flow path 20 from the outer surface 14 to the inner surface 18 and has a downstream edge 35. The outer casing 12 and the inner casing 16 include openings 36, 38, respectively, through the surfaces 14 and 18 for accommodating the spindles 32, 34. Also disposed within the openings 36, 38 are bushings 40 within which the spindles 32, 34 rotate with a minimum of friction. In this embodiment the outer spindle 32 extends radially outwardly until it is external of the outer casing 12 where it is connected by an actuation torque arm 42 to a unison ring 44 which is in turn connected to a hydraulic cylinder 46. The hydraulic cylinder 46 rotates the unison ring 44 which moves the actuation torque arm 42 thereby rotating the airfoil 30 and all other airfoils 30 which are connected to the unison ring 44 in a similar manner.

The downstream stationary portion 28 includes an airfoil 48 and outer and inner lugs 50, 52, respectively, which are somewhat thicker than the airfoil. The airfoil 48 also has a forward edge 53. Each of the lugs 50, 52 fit tightly into slots 56, 58 in the outer and inner casing 12, 16, respectively (see FIG. 2). This purely mechanical connection between the lugs 50, 52 and the casing l2, l6 permits easy removal and/or replacing of individual stationary portions 28 which would not be possible if they were welded or brazed into place. The lugs 50, 52 extend only over the rearward portion of the air foil 48 since the forward portion extends between the spindles 32, 34 which rotate during engine operation.

As is apparent from the drawing, the spindles 32, 34 have a common axis of rotation herein designated by the numeral 60; in this embodiment the axis 60 lies along a radial line. Note, also, that the axis of rotation 60 is downstream of the downstream edge 35 of the airfoil 30. Each of the spindles 32, 34 includes a cylindrical cavity 64, 66, respectively, centered on the axis of rotation 60 and in communication with the gas path 20. The airfoil 48 includes pins 68, 70 integral therewith and extending radially from the forward edge 53 into the cavities 64, 66. The pins 68, 70 have an anti-friction coating thereon to permit smooth rotation of the spindles 32, 34. in this particular embodiment, without the pins 68, 70 the forward portion of the airfoil 48 would be unsupported and would have a vibration problem. Also, a minimal gap between the downstream edge 35 and the forward edge 53 can be obtained because the axis of rotation is coincident for both the movable and stationary portions of the vane. The pins 68, 70 of the stationary portion 28 engage cavities 64, 66 in the variable portion; the axis of rotation 60 is the common datum from which the edges 35, 53 can be held with small tolerances thus resulting in a minimal gapv A small gap is desirable to minimize air leakage from the pressure to the suction side of the airfoils without me chanical seals. In this embodiment the edges 35 and 53 are continuous and parallel, and the gap therebetween remains substantially constant in size during rotation of the movable portion 30.

The problem of assembly of the stationary portion 28 to the movable portion 26 is solved by a slot 74 (FIG. 2) in the inner spindle 34. The slot extends from the gas path 20 radially inwardly all the way through the spindle 34 and it extends in an axial direction from the cavity 66 through the external surface 76 of the spindle 34. The slot 74 is narrower than the pin 70 but is wider than the forward edge 53 at least near the radially inner portion thereof. At assembly the radially inner portion of the forward edge 53 of the airfoil 48 is inserted into the slot 74; the stationary portion 28 is then slid toward the outer spindle 32 until the pin 68 engages the cavity 64 and the pin is positioned within the cavity 66.

Since in this embodiment there is a requirement that there be virtually no openings in the gas flow path walls (surfaces 14, 18) and that the flow path be as smooth and continuous as possible, a plug 78 (shown separately in perspective in FIG. 3) is disposed within the inner spindle 34 to fill the slot 74. A retaining ring 79 keeps the plug in place. Although a plug is used in this embodiment, other techniques for filling the slot 74 to eliminate the opening at the gas flow path wall may also be used such as by filling the slot 74 with a suitable rubber like compound.

Further in regard to the requirement that there be as smooth and as continuous a flow path as possible, the outer spindle 32 and the inner spindle 34 include surfaces 80, 82, respectively, which are circular and which extend across the openings 36, 38 so that the gas flow path is streamlined and essentially unbroken in the area where the stator vane is attached to the casing.

Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and the scope of the invention.

Having thus described a typical embodiment of my invention, that which I claim as new and desire to secure by Letters Patent of the United States is:

l. A variable stator vane assembly for turbomachinery comprising:

casing means including inner annular casing means having inner surface means and outer annular casing means having outer surface means, said inner and outer surface means defining an annular gas flow path therebetween;

a plurality of stator vanes circumferentially spaced within said flow path, each including a radially extending airfoil, said airfoil including a downstream stationary portion extending from said inner to said outer casing means and an upstream movable portion extending from said inner to said outer casing means, said movable portion including a continuous downstream edge, each of said stator vanes also including an inner spindle and an outer spindle, said inner and outer surface means each including openings therein for accommodating said spindles, said spindles being rotatably disposed therein, each spindle including a circular surface extending across said opening, said inner and outer spindles of each vane also having a common axis of rotation rearward of said downstream edge, said movable portion of said airfoil being fixedly secured to both said inner and outer spindles for rotation therewith, said circular surfaces having a diameter larger than the thickness of said airfoil and overhanging said downstream end of said movable portion, each of said spindles having a cavity therein open at said circular surface thereof and centered on said spindle axis of rotation, said stationary portion of said airfoil having a forward portion and a rearward portion, said rearward portion being secured to said casing means, said forward portion including pin means extending into said cavities of both said inner and outer spindles, said pin means having an axis common to said spindle axis of rotation; and

actuation means connected to said stator vanes for rotating said movable portions thereof.

2. The stator vane assembly according to claim 1 wherein said stationary portion of said airfoil includes a leading edge, said leading edge having an outer end and an inner end, and said pin means includes a first pin extending radially outwardly from said outer end of said leading edge into said cavity of said outer spindle and a second pin extending radially inwardly from said inner end of said leading edge into said cavity of said inner spindle, said downstream edge of said movable portion being parallel and adjacent to said leading edge of said stationary portion there being only a small gap therebetween which remains substantially constant in size during rotation of said movable portion.

3. The stator vane assembly according to claim 2 wherein said rearward portion of said stationary portion of said airfoil is mechanically secured to said inner casing means and to said outer casing means.

4. The stator vane assembly according to claim 1 wherein said openings in said inner and outer surface means are completely filled by said stator vanes and said flowpath is streamlined and substantially continuous in the area of said stator vanes.

5. The stator vane assembly according to claim 4 wherein at least one of said spindles of each stator vane includes a slot extending through said spindle in the direction of the axis of rotation and being in communication with said spindle cavity, said slot being wide enough to pass over said leading edge of said stationary portion of said airfoil at assembly of said stator vanes for permitting engagement of said pin means into said cavities of both said inner and outer spindles, and plug means disposed within said slots for keeping said flow path substantially unbroken in the area of said stator vanes. 

1. A variable stator vane assembly for turbomachinery comprising: casing means including inner annular casing means having inner surface means and outer annular casing means having outer surface means, said inner and outer surface means defining an annular gas flow path therebetween; a plurality of stator vanes circumferentially spaced within said flow path, each including a radially extending airfoil, said airfoil including a downstream stationary portion extending from said inner to said outer casing means and an upstream movable portion extending from said inner to said outer casing means, said movable portion including a continuous downstream edge, each of said stator vanes also including an inner spindle and an outer spindle, said inner and outer surface means each including openings therein for accommodating said spindles, said spindles being rotatably disposed therein, each spindle including a circular surface extending across said opening, said inner and outer spindles of each vane also having a common axis of rotation rearward of said downstream edge, said movable portion of said airfoil being fixedly secured to both said inner and outer spindles for rotation therewith, said circular surfaces having a diameter larger than the thickness of said airfoil and overhanging said downstream end of said movable portion, each of said spindles having a cavity therein open at said circular surface thereof and centered on said spindle axis of rotation, said stationary portion of said airfoil having a forward portion and a rearward portion, said rearward portion being secured to said casing means, said forward portion including pin means extending into said cavities of both said inner and outer spindles, said pin means having an axis common to said spindle axis of rotation; and actuation means connected to said stator vanes for rotating said movable portions thereof.
 1. A variable stator vane assembly for turbomachinery comprising: casing means including inner annular casing means having inner surface means and outer annular casing means having outer surface means, said inner and outer surface means defining an annular gas flow path therebetween; a plurality of stator vanes circumferentially spaced within said flow path, each including a radially extending airfoil, said airfoil including a downstream stationary portion extending from said inner to said outer casing means and an upstream movable portion extending from said inner to said outer casing means, said movable portion including a continuous downstream edge, each of said stator vanes also including an inner spindle and an outer spindle, said inner and outer surface means each including openings therein for accommodating said spindles, said spindles being rotatably disposed therein, each spindle including a circular surface extending across said opening, said inner and outer spindles of each vane also having a common axis of rotation rearward of said downstream edge, said movable portion of said airfoil being fixedly secured to both said inner and outer spindles for rotation therewith, said circular surfaces having a diameter larger than the thickness of said airfoil and overhanging said downstream end of said movable portion, each of said spindles having a cavity therein open at said circular surface thereof and centered on said spindle axis of rotation, said stationary portion of said airfoil having a forward portion and a rearward portion, said rearward portion being secured to said casing means, said forward portion including pin means extending into said cavities of both said inner and outer spindles, said pin means having an axis common to said spindle axis of rotation; and actuation means connected to said stator vanes for rotating said movable portions thereof.
 2. The stator vane assembly according to claim 1 wherein said stationary portion of said airfoil includes a leading edge, said leading edge having an outer end and an inner end, and said pin means includes a first pin extending radially outwardly from said outer end of said leading edge into said cavity of said outer spindle and a second pin extending radially inwardly from said inner end of said leading edge into said cavity of said inner spindle, said downstream edge of said movable portion being parallel and adjacent to said leading edge of said stationary portion there being only a small gap therebetween which remains substantially constant in size during rotation of said movable portion.
 3. The stator vane assembly according to claim 2 wherein said rearward portion of said stationary portion of said airfoil is mechanically secured to said inner casing means and to said outer casing means.
 4. The stator vane assembLy according to claim 1 wherein said openings in said inner and outer surface means are completely filled by said stator vanes and said flow path is streamlined and substantially continuous in the area of said stator vanes. 